Geotechnical Engineering

DHARM

868 GEOTECHNICAL ENGINEERING

Amplitude of vibration of the anvil

Aa = −

−

−

()

()

ωω

ωωω

an

nnn

va

2

1

2

1

2

2

2

2

= −

−

−

()×

(.)(.)

(^253272).
272 54 3 54 3
0 643
22
22 m = 1.66 mm
Example 20.10: Design a suitable block foundation for a two-cylinder vertical compressor for
the following data:
crank angles: 0 and π/2
Weight of compressor = 200 kN
operating speed: 600 rpm
Total weight of rotating mass: 0.06 kN
Total weight of reciprocating mass: 0.27 kN
Radius of crank: 0.4 m
safe bearing capacity of soil under static conditions: 100 kN/m^2
coefficient of elastic uniform compression: 45,000 kN/m^3
Calculation of Unbalanced Inertial Forces
crank angles 0 and p/2.
The crank mechanisms of both cylinders are taken to be identical. Resultant unbal-
anced inertial force in the vertical direction
Pz = (Mrec + Mrot)Rω^2 cos (ωt + π/4)
Mrec =
027
981
.
.
kN sec^2 /m Mrot =
006
981
.
.
kN sec^2 /m
∴ Pzmax =^2
033
981
04
600
60
2

.^2
.

F.

HG

I

KJ

×× ×F

HG

I

KJ

π kN

= 75.124 kN

Similarly Px also may be calculated.

Px = MRrot ωωt

2 π

4

sinFHG + IKJ

∴ Pxmax =^2

006

981

04

600

60

2

2

××× ×FHG IKJ

.

.

. π kN

= 13.7 kN.

Size of Foundation

Let us assume a block of size 6 m × 3 m × 1 m high for a compressor foundation.

The compressor and motor should be so arranged that the eccentricity of the resultant

forces due to the weight of the machine and foundation block do not exceed 5%.

Weight of foundation block = 6 × 3 × 1 × 24 = 432 kN

(assuming the unit weight of concrete as 24 kN/m^3 )